In 793 the monks on the island of Lindisfarne, off the northeast coast of England, are unpleasantly surprised by the arrival of violent raiders from the sea. Their misfortune is the first clearly dated event in the saga of the Vikings - the last and most dramatic exodus in the long story of migration from Scandinavia, the original home of the Goths and Vandals.

The name Viking is thought to derive from vikingr, a word for 'pirate' in the early Scandinavian languages. It accurately describes the Norsemen who for two centuries raid the coasts of Britain and of northwest France. But in many places the Scandinavians also settle - in the islands of the north Atlantic, in the British Isles, in Normandy, in Sicily and in the very heart of Russia.

It is impossible to assign the various Viking groups at all precisely to places of origin. But broadly speaking, adventurers from the coast of Norway raid the north of England and continue round the Scottish coast to Ireland. Vikings from the same region later settle in the Scottish islands, Iceland and parts of Ireland.

The Vikings invading eastern Britain and northwest France, and eventually settling in both regions, come mainly from Denmark. The Swedes raid across the Baltic and penetrate deep into Russia as traders.

The Vikings and the British Isles: 9th - 10th century

The coasts of the British isles are now dotted with monasteries, not yet rich by the standards of medieval monasticism but with sufficient wealth to attract Viking marauders. One of the most famous islands, Iona, is raided three times in a decade (in 795, 802 and 805). Even monasteries which seem secure, pleasantly sited on inland rivers, fall victim to Viking longships rowing upstream. But gradually, during the 9th century, the raiders settle.

Soon all the Scottish islands and the Isle of Man are in Viking hands, and the intruders are even seizing territory on the mainland of both Britain and Ireland. In 838 Norwegians capture Dublin and establish a Norse kingdom in Ireland. From 865 the Danes settle in eastern England.

Danes in England: from865

Thirty years of Danish raids on the east coast of England precede the arrival, in 865, of a 'Great Army' equipped for conquest rather than quick booty. The Danish invaders now consolidate each year's gains by establishing a secure base from which they can continue a campaign of harassment - which invariably ends with the settled English buying peace from their footloose tormentors.

York is taken in 866 (and becomes, as Yorvik, the Danish capital in England). Nottingham falls in 867, Thetford in 869. By now the kings of Northumbria, Mercia and East Anglia have made terms with the invaders. Next in line is Wessex.

In 870 the Danes advance into Wessex, capturing Reading where they meet the most determined opposition thus far. During the next year nine battles are fought in this district. In 871, at Ashdown on the Berkshire downs, the English win their first significant victory of the war; a Danish king and nine earls are killed on the field of battle. Even so, it proves impossible to recapture Reading. Wessex, like the other English kingdoms, makes peace with the Danes - who withdraw to winter in London.

But the victory at Ashdown has introduced a figure of significance in English history. The Wessex men are commanded that day by a 23-year-old prince of their ruling family - Alfred, brother of the king of Wessex.

Alfred and the Danes: 871-899

In popular tradition the story of England, as opposed to Britain, begins with Alfred. And there is a valid basis for this heroic status. He is the first Anglo-Saxon ruler to be accepted as something akin to a national leader. The English see him as such in those regions resisting Danish domination. With good cause he is the only king of England to be accorded the title 'the Great'.

His authority derives from his successes against the Danes. His kingly virtues can also be seen, with hindsight, in his encouragement of learning. But his central achievement is the quarter-century of struggle which follows his victory over the Danes at Ashdown in 871.

In that same year, 871, Alfred's elder brother dies and he becomes the king of Wessex. One of his first acts is to establish the beginnings of an English fleet. The Danes draw much of their strength from their swift Viking longships. It makes sense for the Anglo-Saxon islanders to reply in kind. By 875 Alfred can claim a small naval victory which is nevertheless a significant beginning. Going to sea with his new fleet, he holds his own against seven Danish ships and even captures one of them.

On land he has similar successes, defeating Danish armies and forcing them to agree to leave Wessex in peace. But the Danes regularly break their word.

In 878 a surprise Danish attack pushes Alfred west into the Somerset marshes. From a single fort at Athelney he organizes local resistance. This is the lowest ebb of the English cause, the nearest that the Danes come to conquering Wessex and establishing their rule over the whole of England.

Within a few months Alfred is strong enough to move east again and defeat the Danes at Edington in Wiltshire. The conclusion of this campaign is a two-week siege of Guthrum, the Danish king of East Anglia, who is encircled in his encampment. Guthrum secures his freedom by promising (once again) to leave Wessex. More significantly, he also agrees to be baptized a Christian.

The ceremony of baptism takes place on the river Parrett, with Alfred in the role of sponsor of the new convert. Then the two Christian kings go together to Wedmore (the year is still 878), where they spend twelve days in ceremony and feasting and in the agreement of a treaty which finally preserves Wessex from Danish intrusion.

A Danish invasion of Kent in 885 gives Alfred the pretext for expansion eastwards. He drives back the invaders, and in 886 occupies London. This success leads to a new treaty with Guthrum. He and Alfred agree a basis for coexistence between Anglo-Saxons in the south and west and Danes in the north and east of the country - the region which becomes known as Danelaw.

Norwegians in Ireland: 9th - 11th century

During the 9th century the Norse kings of Dublin are in constant warfare with Irish kings. They suffer several reverses. But in the early 10th century the trend seems to be going in favour of the Vikings. They capture important strongholds at the mouths of Ireland's main rivers. Waterford falls to them in 914, Limerick in 920. Cork is at various times occupied by Vikings, and Wexford is founded as a Norse settlement.

The Irish persistently fight back - most notably under the leadership of Brian Boru.

Brian Boru and the Vikings: 976-1014

Brian, known as Boru from his birthplace by the river Shannon, is the son of a small local ruler. His family gain power through their successful attacks on the Vikings. In 964 Brian's elder brother asserts his dominance over the local Irish potentates, the royal dynasty of Munster. Taking their famous stronghold, the rock of Cashel, he becomes accepted as king of Munster and as leader of resistance to the Vikings in southern Ireland. Brian succeeds him in both roles in 976.

Brian Boru successfully drives the Vikings from the Shannon. In 1002 he is accepted as high king of all Ireland. His final confrontation with the Norsemen follows a plot set in motion in 1013.

In 1013 the Norse king of Dublin spends Christmas in the Orkneys with another Viking ruler - the local earl. They hatch a scheme. The earl of the Orkneys will bring a fleet and army to Dublin, before Easter, to assist the Norse king in overwhelming the king of all Ireland, Brian Boru.

The engagement takes place, and at the appointed season. On April 23, 1014, Brian Boru confronts the Norse army at Clontarf, on the coast just east of Dublin. He is now seventy-three, so he only directs the battle. His son, Murchad, leads the men in the field and dies fighting (as does the earl of the Orkneys). After twelve hours the Norsemen are defeated. But a Viking chieftain, fleeing the battlefield, comes across Brian Boru in his tent and kills him.

The Irish victory at Clontarf puts an end to any serious Norse threat to the whole of Ireland. But it does not remove the Vikings from their coastal strongholds of Dublin and Waterford. And, with both Brian Boru and his son casualties of the battle, it leaves the Irish themselves in a disordered state.

This remains the case for more than a century until a stronger group of Vikings, of Norman descent, arrive on the Irish coast in 1169.

Vikings in the North Atlantic: 9th - 10th century

Rowing and sailing through the northern seas, in their superbly streamlined longships, the Norsemen settle in islands close to land which have been inhabited since neolithic times (such as the Orkneys and Shetlands) and in others further afield where their only predecessors - in the previous century or two - are Irish Christian hermits, searching for isolated discomfort.

Islands with only hermits to displace include the Faeroes and above all Iceland. From Iceland the Vikings venture even further west to perch on the edge of Greenland, where they are preceded only by the Eskimo.

The first family of Iceland: 874

In 874 Viking longships are beached on a promontory in the southwest of Iceland, where Reykjavik now stands. They have brought from the coast of Norway a chieftain, Ingólfur Arnarson, together with his family, dependents and livestock. Arnarson establishes a settlement, based on fishing and sheep farming.

Other similar groups soon follow, staking out territories round the coast of the island. Two centuries later the population of Iceland is already about 75,000 people - a level not exceeded until the 20th century. Meanwhile Norse colonists from Iceland have formed the first European settlements on the American continent, naming them Greenland and Vinland.